Turkey’s president, Recep Tayyip Erdogan, has gall. He has jailed tens of thousands of people, shuttered more than 150 media companies and called a referendum in April to enlarge his powers. Yet when local authorities in Germany, for security reasons, barred two Turkish ministers from campaigning on his behalf among Turks living in Germany, Mr. Erdogan exploded, accusing Germany of Nazi practices and knowing nothing about democracy. If he himself was barred from speaking in the country, he warned, he’d “set the world on fire.”

This is all the more galling knowing that among the scores of journalists jailed in Turkey is a reporter for Die Welt, with German and Turkish citizenship, whom Mr. Erdogan has accused of being a German spy and a “representative” of an outlawed Kurdish rebel group. Some furious German politicians have urged Chancellor Angela Merkel to tell Mr. Erdogan that he is not welcome in Germany. Properly, and wisely, she has not. Appearances by leading Turkish politicians, she said, “remain possible within the laws applicable here.” Permits for demonstrations are handled locally, though, and Ms. Merkel said she has no say in them.

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Ms. Merkel does have security reasons for her restraint: Germany uses a NATO base in Turkey for reconnaissance aircraft in the fight against the Islamic State, and Ms. Merkel was the key force behind a European Union deal with Ankara by which Turkey helps stem the flow of refugees into Europe. But more important, Germany does not want to stoop to Mr. Erdogan’s level.

Though Germany is arguably among the most law-abiding and tolerant of the European democracies, the Germans must regularly contend with reminders of their Nazi past, especially by countries like Greece, Poland or Hungary that find themselves on the receiving end of European Union admonishment or censure. For the leader of a major nation and NATO ally to hurl such insults, however, especially when Mr. Erdogan himself has done so much to subvert freedom of speech and the rule of law in Turkey, is outrageous.

The estimated 1.5 million Turks in Germany eligible to vote in the Turkish referendum are obviously of major interest to Mr. Erdogan. The fact that Germany provides so many Turks with a livelihood argues against Mr. Erdogan’s accusations, while barring his surrogates from campaigning among them, as local authorities did, only gives him fodder.

The better response is to continuously remind Mr. Erdogan, his surrogates and his people that the freedoms so many Turks find in Germany are being systematically and shamelessly destroyed in Turkey.